Rust is one of the harder languages for beginners to learn because of its borrow checker and strict ownership model, but it shouldn't take more than a month or two for a competent senior to pick up.
It's going to be deeply unpleasant and seem like a problem if:
- You're writing dangerously bad C or C++ code already.
- You've only ever used Python or JavaScript.
- You try to shoehorn OOP and inheritance into it (Rust idioms are composition and functional programming).
- You refuse to use/learn pattern matching.
- You're a pedant about "pretty" syntax.
If someone is at a senior level and any of those apply, they probably shouldn't be at a senior level, though.